I've read a couple of interesting threads on here about lightened flywheels recently, the 'modern' way of doing this seems more effective at reducing weight and probably stronger / less risky than drilling millions of holes like they used to back in the day.
So, where does that leave the 'Swiss cheese' type? I always had doubts about weakening the thing and I'm not sure how far you can safely go. Do we know of any cases where a drilled flywheel has failed? Is there a critical area to avoid?
I only ask because I have a drilled flywheel in one of my boxes and I'm wondering whether to hang onto it or not. Will become pertinent soon as I'm building up an engine which is currently short of a (Ruby/ Newton Bennett) flywheel and clutch assy.
Thoughts welcomed...and yes I'll put up a pic when I get a moment...
Joined: Aug 2017 Posts: 381 Threads: 16
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8 Location: Port Elizabeth, Sunny South Africa
Car type: '26 Chummy, '28 Top Hat, '33 Type "65", single seaters
Hi Chris, when we rebuilt the motor of the green single seater we lightened the flywheel by 2.5 lbs as that is what the 750 bulletins of the '50's recommended, it worked so well that we did the same when built the blue supercharged single seater, HOWEVER, both are race cars so the ring gear came off as did some material from the back of the flywheel and the edges were all rounded to loose weight & we thinned the pressure plate to just the width of the clutch lining
It worked for our purposes as both cars rev easily to 6000 rpm, however for a road car I wouldn't suggest more than 0.5 to 1.5 lbs - the middle road of 1 lbs would make a positive difference in revs, but without sacrificing the rotational inertia needed for smooth ascending of hills etc. This is one of those cases where less is more, so even 0.8 lbs would be good.
Probably the single biggest improvement you can make is to balance the motor - crank, rods, pistons flywheel & pressure plate
That and meticulous assembly where you make 100% sure that the oil jets squirt into the crank pockets by doing the pump paraffin exercise - try get hold of the Mike Forrest double oil conversion bulletin - you can stick to single jets, but bend them as Mike suggests to ensure that 90*+ of the crank rotation is being fed oil = maximum survival for the motor. A little over-bore on the oil pump won't hurt either.
(26-12-2018, 04:20 PM)Greig Smith Wrote: Hi Chris, when we rebuilt the motor of the green single seater we lightened the flywheel by 2.5 lbs as that is what the 750 bulletins of the '50's recommended, it worked so well that we did the same when built the blue supercharged single seater, HOWEVER, both are race cars so the ring gear came off as did some material from the back of the flywheel and the edges were all rounded to loose weight & we thinned the pressure plate to just the width of the clutch lining
It worked for our purposes as both cars rev easily to 6000 rpm, however for a road car I wouldn't suggest more than 0.5 to 1.5 lbs - the middle road of 1 lbs would make a positive difference in revs, but without sacrificing the rotational inertia needed for smooth ascending of hills etc. This is one of those cases where less is more, so even 0.8 lbs would be good.
Probably the single biggest improvement you can make is to balance the motor - crank, rods, pistons flywheel & pressure plate
That and meticulous assembly where you make 100% sure that the oil jets squirt into the crank pockets by doing the pump paraffin exercise - try get hold of the Mike Forrest double oil conversion bulletin - you can stick to single jets, but bend them as Mike suggests to ensure that 90*+ of the crank rotation is being fed oil = maximum survival for the motor. A little over-bore on the oil pump won't hurt either.
Aye
Greig
No jets on my engine Greig!
Your thoughts on amount of mass to remove are instructive, thanks for that. I will either weigh the assembly or perhaps work it out by adding up how much has been removed (the former might be safer).
It's for a road-going car though and I'm more concerned to understand how much you can get away with from a strength viewpoint when chain drilling a flywheel & clutch. Used to be fairly common practice I believe so must be some experience out there.
Joined: Aug 2017 Posts: 381 Threads: 16
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8 Location: Port Elizabeth, Sunny South Africa
Car type: '26 Chummy, '28 Top Hat, '33 Type "65", single seaters
My radically lightened flywheel knowledge comes from the '50's and '60's Alfa's and talented Engineering friend. Basically 'grenading' flywheels generally only occurs when they are thinned down radically front to back to reduce weight. Additional issues can occur when the mounting points for the hold down bolts are left as pedestals and the material in between is removed and the corners are not radiused properly to relieve the stresses.
I'd suggest you posted a picture of your Swiss cheese flywheel and its weight and we can get a kindly soul to weigh a standard flywheel and all add our 2p in from there
Mine was modified (not by me) as Greig says. Chunks taken out the sides leaving the bolt holes as mounts. The corners are radiused on it. I have no idea how much weight that saves or what the effect will be in the car. I did have everything balanced though. I think that is definitely worth doing and I'll always do that on an engine I am building now.
(26-12-2018, 09:12 PM)jansens Wrote: Mine was modified (not by me) as Greig says. Chunks taken out the sides leaving the bolt holes as mounts. The corners are radiused on it. I have no idea how much weight that saves or what the effect will be in the car. I did have everything balanced though. I think that is definitely worth doing and I'll always do that on an engine I am building now.
Simon
If you can get away with that I doubt I have much to worry about!
I'll try & get a pic up tomorrow.
Joined: Aug 2017 Posts: 381 Threads: 16
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8 Location: Port Elizabeth, Sunny South Africa
Car type: '26 Chummy, '28 Top Hat, '33 Type "65", single seaters
Simon that lightened flywheel of yours looks a proper job, radiused corners are right, it's probably a pound lighter, and you still have a full pressure plate + ring gear
For a road car this is perfect, its definitely a case of less-is-more when lightening road car flywheels, too much off and you loose rotational inertia and you literally have nothing to carry the car up a slight bump, on a race car where the throttle response is much like an on-off switch this isn't an issue, but having an all or nothing motor in a road car is miserable. The flywheel on our '28 Model A is a colossal thing, we actually lifted it up with the engine crane before fitting it. A friend lightened his one and while it revs faster, our A is actually quicker on the road as we can climb hills in top while he is bleeding off speed while scratching for 2nd gear... and with a 3.3 litre engine, torque is your secret weapon.
With the mouse motors in our Sevens, you need a little rotational inertial to carry you up the inclines, the standard flywheel does very well, but a just a little rotating mass off, makes a big difference in rev response when shifting gears. It's probably the second most noticeable thing you can do the the motor, the biggest is to balance the motor. Despite the blue race car being an offset single seater with an offset short prop shaft and a Yamaha 650 shaft drive and universal joint driven off the nose of the crank to put the blower straight out front, it's probably the smoothest 7 engine we've ever built, but I balanced everything meticulously - you can see where I ground the casting flashing on the big end caps to equalise the weights of the rods, they were also balanced end to end. The pistons were balanced to 0.1g as were the rods and then the whole assembly was taken to an engineering works for balancing.
This is the flywheel from the Green Job - 2.5lbs lighter than standard as per the period 750 Bulletins, no ring gear and lightened pressure plate, so no need for the pedestal machining as we are already at target weight - the rev response is fantastic, it spins to 6000 with ease. The Blue job looks much the same - I'll report back after the Simola Hillclimb !!
Unlike most modern cars, the A7 flywheel is steel rather than cast iron, it's a pretty tough steel at that, as anyone who has machined one will be able to confirm. I can't imagine one letting go unless something quite reckless has been done in terms of lightening it. I have done the "pillaring" of the flywheel rim on road car motors as per Simon's in the post above and they have still been perfectly driveable afterwards. Lightening what is quite a heavy flywheel setup not only makes the motor more responsive, it also gives the crankshaft an easier time.
(27-12-2018, 02:25 PM)Charles P Wrote: Stuart, any idea how much weight is saved with the "pillaring" approach?
Thanks
Charles
For road motors, I cut straight across the flywheel rim with a 2" carbide insert cutter, so the pillars end up wider than those on Simon's flywheel. this takes about 1 3/4 lb off the flywheel weight.
